Studies will be conducted to elucidate the developmental interrelationships of putative neurotransmitters in the rat brain. The metabolism of putative neurotransmitters will be altered at specific periods of neurochemical maturation during gestational or neonatal stages. This will be accomplished in two ways: (1) by placement of discrete lesions in the nuclei of original neurons containing dopamine, norepinephrine, serotonin, acetyl-choline or gamma-amino butyric acid on 10, 21 and 39 day old rats, and (2) with the use of drugs that are known to act by altering the activity of neurons containing biogenic amines, acetylcholine or gamma-amino-butyric acid. The hypothesis that the manipulation of biochemical and morphological differentiation during gestational or neonatal stages of growth has long-lasting and permanent consequences on normal neurochemistry of brain will be tested. Another study will be conducted to elucidate the effects of the chronic administration of antidepressant drugs and L-dopa during gestation and first few weeks after birth. Corticosteroids will be administered, in addition, to some rats during the first five days after birth. The hypothesis will be tested that elevation of biogenic amines at a specific period during neurochemical maturation may permanently alter the capacity of the neuron to synthesize amines and that corticosteroids may induce N-methylating enzymes in the brain to form potentially psychoactive metabolites of biogenic amines.